EP0731333B1 - Multi-coordinate feeler head with equal displacements - Google Patents

Abstract

The sensor head has at least one movable sensor pin (2), deflected from its zero position upon contact with the workpiece against the force of a return bias. The deflection of the sensor pin relative to the sensor head housing is detected at the opposite end to the workpiece, to provide a corresponding deflection signal. The sensor pin is supported by a multi-point bearing with a geometry matched to the geometry and material characteristics of the workpiece, to ensure uniform deflection of the sensor pin in all directions.

Description

The invention relates to a multi-coordinate probe according to the preamble of claim 1.

Multi-coordinate probes are from various publications known. All have sensors that deliver a probing signal when probing an object. The type of sensors is different: It can be electrical switches, for example, or photoelectric measuring systems or distance sensors. Find such embodiments in DE-23 47 633-C3; DE-35 08 396-C1; EP-0 361 164-A1; EP-0 598 709 A.

When probing objects by means of such The multi-coordinate probe becomes one that touches the object Stylus deflected on his free end carries a probe ball. The design of the Sensors and the storage of the stylus conditional it that the generation of a probing signal after more or less deflection of the stylus triggered becomes.

This leads to measurement uncertainty. In addition to a variety the stylus bending plays a role in other factors a major role. For bending the stylus the measuring forces are primarily responsible, the decisive factor through the storage of the stylus be determined.

Measuring force fluctuations cause different Stylus geometry also different bends, which in turn leads to larger or smaller ones Deviations.

There is a linear relationship between deflection and measuring force. This relationship can be formulated according to the equation known from strength theory f = F * 64 3 π E * T L 3rd T D 4th with f: deflection, F: force, E: modulus of elasticity, T _L : clamping length (stylus length), T _D : stylus diameter for the cantilever beam.

The invention is based, with a multi-coordinate probe by bending the stylus to eliminate measuring errors decrease so far that it is negligible becomes small.

This task is done by a multi-coordinate probe solved with the features of claim 1. With the features of the dependent claims Multi-coordinate probe designed even further.

The particular advantages of the multi-coordinate probe according to the invention lie in its simple Construction, which is nevertheless a scanning direction error compensation guaranteed.

Based on the drawings, the invention is described with the help of an embodiment explained in more detail.

Figur 1

einen Mehrkoordinaten-Tastkopf;

Figur 2

ein Prinzip-Schaubild;

Figur 3

ein weiteres Prinzip-Schaubild und

Figur 4

ein Auslenkungs-Diagramm.

It shows

Figure 1

a multi-coordinate probe;

Figure 2

a principle diagram;

Figure 3

another principle diagram and

Figure 4

a displacement diagram.

In Figure 1, the entire basic structure of a Multi-coordinate probe can be seen. This The button shown is designed as a switching button. Through a shaft 1, the button can be in a Spindle of a measuring or processing machine, not shown be used. The deflection a stylus 2 is possible in all directions. A seal 3 closes the gap between a probe housing 4 and the stylus 2nd

A detector arrangement 7, 8, 9 for detecting the Deflection of the stylus 2 gives a certain Deflection amount a probing pulse, which is used to control a machine tool Determination of the point in time of the acceptance of the measured value a coordinate measuring machine is used or serves another measurement purpose. The detector arrangement 7, 8, 9 consists of one in the probe housing 4 fixed optical transmitter 7 and one also aligned fixed differential photo element 8. In the optical axis of the two elements 7, 8 is a lens system 9 fixed on movable stylus 2 attached.

A measuring plate 10 is firmly connected to the stylus 2, which has a probe ball 11 at the end. An area of the measuring plate 10 stands with the Probe housing 4 by means of a spring 12 in connection. The counter surface is part of the storage of the Measuring plate 10 in the probe head 13th This Storage must be carried out exactly, as a static Under- or overdetermination caused measurement errors.

During a probing process on a workpiece 0 the measuring plate 10 by the spring 12 in place and Position - that is, in its zero position - held, the force of the spring 12 being the effect of the contact pressure the probe ball 11 on the workpiece 0 counteracts, and prevents the measuring plate 10th is pivoted or lifted in the storage, if this force is below a certain value. As long as the measuring plate 10 against the probe housing bottom 13 is held by the spring 12, form Measuring plate 10 and probe housing 4 a unit with the degree of freedom zero. After completing a deflection acts the spring 12 so stressful that it the measuring plate 10 against the probe housing bottom 13 leads back.

The storage, designed as a multi-point storage - here as a three-point bearing - consists of evenly over the scope of the measuring plate 10 more distributed and in a plane arranged balls 14 which are fixed in the Measuring plate 10 are anchored. Each of the balls 14 is a suitable counter bearing, here a prism 15 with a V-shaped groove 16 assigned.

The prisms 15 are aligned so that their V-groove 16 perpendicular to the longitudinal axis of the one resting in the zero position Stylus 2 runs so that each ball 14th defined to lie in the assigned V-groove 16 is coming.

Figure 2 shows a schematic diagram in which the geometric conditions for a three-point bearing Multi-coordinate probe shown in Figure 1 are.

Such touch probes (multi-coordinate probes) with three-point bearing are statically determined and easy to manufacture. However, they have the peculiarity that the deflection forces depending on the direction spread the factor 2. Because of these different The stylus 2 becomes deflecting forces during the probing process bent differently. This fact is detailed in the magazine "Technisches Messen tm "in volume 2 of year 1979 in the Article "Determination of the measurement uncertainty of 3-D touch probes" described.

With a three-point bearing, the work is about Stylus 2 or the measuring plate 10 up to the switching point deflect equally in all directions.

The two multipliers that make up the work calculated will change in the worst case Fall by a factor of 2.

The deflection path is due to the lever laws large and the force required is small or it is the deflection path is small and the force required large.

To ensure even switching behavior across the range of 360 °, that is, to get out of everyone The same switching characteristic (Scanning direction characteristic) must be obtained same deflection paths for the probe ball 11 reached become.

Deflection is to be understood as the way which the probe ball 11 from the touch of the Workpiece (object) 0 until the deflection signal is triggered through the sensor 7, 8, 9 got to.

The deflection paths S _R are composed of partial paths, namely the bending path S _V and the release path S _A. Before the stylus 2 is tilted by the probing process to the object 0 from one of its positions 14/16, the stylus 2 bends to a certain extent, which is dependent on the probing forces F ₁ , F ₂ .

The sensor 7, 8, 9 is located above the plane in which the locations 14/16 are located. The lens system 9 is located on the measuring plate 10 of the stylus 2. By probing the stylus 2 on the object 0, the measuring plate 10 is tilted out of its parallel plane, the plane in which the positions 14/16 are located, and if the lens system 9 is tilted sufficiently, the lens system 9 so displaced that the sensor (detector arrangement 7, 8, 9) generates a deflection signal. The extent to which the lens system 9 has to be displaced in order to produce a deflection signal is constant for the exemplary embodiment and is referred to as the stroke with l ₅ .

Due to the bearing geometry, the axes of rotation D ₁ and D _{2 are at} different distances from the axis of the stylus 2. These relationships can also be seen in FIG. 3, in which the distance from the central axis of the stylus 2 to the axis of rotation D _{1 is} denoted by l ₁ and the distance from the center axis of the stylus 2 to the axis of rotation D ₂ by l ₂ , where l ₂ = 2l ₁ is.

In order to achieve the same stroke 1 ₅ for the sensor 7, 8, 9, as can be seen from FIG. 4, the ball 11 of the stylus 2 must be deflected by the path s ₁ when tilted about the axis of rotation D ₁ (position of the ball with Dash-colon line, shown); the deflection for tilting about the pivot point D ₂ must, however, take place by the path s ₂ (position of the ball shown with a dash-dot line). The paths s ₁ and s _{2 are} inversely proportional to the distances l ₁ and l ₂ , with s _{1 being} twice as large as s ₂ . This applies if completely rigid components are accepted.

In order to deflect the stylus 2 or its ball 11 by the above-mentioned paths s ₁ and s ₂ , different forces F ₁ and F _{2 are} required, which are again inversely proportional to the mentioned paths s ₁ and s ₂ .

Different forces F ₁ and F ₂ cause different deflections of the stylus 2. Since - as already explained above - there is a linear relationship between the measuring force and the deflection of the stylus 2, the deflection paths S _V1 and S _{V2 are} proportional to the measuring forces F ₁ and F ₂ .

The release paths S _A1 and S _A2 correspond to the above-mentioned paths s ₁ and s ₂ with completely rigid components.

In order to eliminate the scanning direction characteristic, the deflection paths S _R1 and S _R2 must be of the same size. This means that regardless of the direction of contact, the ball 11 of the stylus 2 must always be shifted by the same amount in order to generate the stroke l ₅ through which the sensor 7, 8, 9 can trigger the contact signal.

But because due to the geometrical arrangement of the bearing points 14/16 - i.e. the mounting of the stylus 2 - the release paths S _A1 and S _{A2 are of} different sizes (they correspond to the paths s ₁ and s ₂ and are therefore inversely proportional to those due to the storage given distances l ₁ and l ₂ ), the bending paths S _V1 and S _V2 must compensate for this inequality of the triggering paths S _A1 and S _A2 . The deflection paths S _R1 and S _R2 must be the same, therefore the sums S _V1 + S _A1 and S _V2 + S _{A2 of} the bending paths S _V1 , S _V2 and the release paths S _A1 , S _{A2 must be the} same (S _R1 = S _V1 + S _A1 = S _R2 = S _V2 + S _A2 ).

In order to achieve the resultant deflection paths S _R1 and S _{R2 of the} same length, the deflection of the stylus 2 must, among other things, be specifically included in the dimensioning of the multi-coordinate probe. The entire deformation parameters of the stylus 2 / bearing 17 unit must be selected such that the probing characteristic is eliminated due to the resulting deflection paths S _R1 , S _R2 .

Deformation parameters of the stylus / Bearings include their geometry, material properties, the stylus modulus, the stylus moment of inertia, the restoring force that too expected material pairing of probe ball and Workpiece because of the flattening and - as far as it Measuring accuracy requires - further properties the named unit.

The calculation formulas for the relationships between the distances l ₁ and l _{2 mentioned} , the stroke l ₅ , the path lengths s ₁ and s ₂ , the triggering paths S _A1 and S _A2 , the deflection paths S _V1 and S _V2 , the resulting deflection paths S _R1 and S _R2 , the length L _{2 of} the stylus 2 and its diameter T _D , the diameter of the ball 11, the moving masses and the geometrical arrangement of the bearing points 14/16 can be derived from the strength theory, the kinematics and especially the lever laws.

In order to bend the stylus 2 by the path S ₁ , a moment M ₁ must act when tilted about the axis of rotation D ₁ , which is equal to the product of the force F ₁₂ times the distance l ₁ , ie M ₁ = F ₁₂ * l ₁ .

This moment is equal to the moment which results from the product of the contact force F ₁ and the length L _{2 of} the stylus 2, so M ₁ = F ₁ * L ₂ .

The bending S ₁ results from changing the equations of the strength theory (see above) S 1 = l 5 * L 2 2 * l 1 = F 1 * L 2 3rd 3E * Θ , where Θ = π * T D 4th 64 is used as the moment of inertia.

Kraft F₁₂ = 10N

Taststiftlänge L₂ = 60 mm

Abstand l₁ = 4 mm

Hub l₅ = 0,003 mm

Taststift-Werkstoff Stahl

E-Modul von Stahl E = 210.000 N/mm²

A numerical example is intended to show the calculation of the stylus diameter T _D in a first approximation. Given are:

Force F ₁₂ = 10N

Stylus length L ₂ = 60 mm

Distance l ₁ = 4 mm

Stroke l ₅ = 0.003 mm

Steel stylus material

Young's modulus of steel E = 210,000 N / mm ²

The moment M ₁ results from M 1 = F 12th * l 1 = 10N * 4 mm M 1 = 40 Nmm = 0.04 Nm

The bend results from S 1 = l 5 * L 2 2 * l 1 = 0.003 * 60 2 * 4 mm S 1 = 0.0225 mm ≈ 22 µm

This bend is the same S 1 = F 1 * L 2 3rd L 2 * 3 * E * Θ = 0.000.022 = 0.04 * 0.06 2 3 * E * Θ Θ = 0.04 * 0.06 2 3 * 0.000022 * 210,000,000,000 Θ = 0.000.01 * 10 -6 m 4th Θ = 0.000.01 * 10 -6 = π * T D 4th 64 T D = 0.003.8 m ≈ 4 mm

For the given sizes, the is calculated Stylus diameter to 4 mm.

Claims (4)

1. Multi-coordinate touch probe having a probe stylus (2) deflectable out of a support which determines its zero position and into which it may be pushed by a resetting force (F12); wherein

   the probe stylus (2) is secured to a measuring plate (10) which is mounted pivotable in a probe housing (4) via rotational axes (D1, D2) forming the support;

   the support is a multi-point support formed from support points (14, 16) located at a spacing from one another;

   as a result of the support points located at a spacing from one another, the forces (F1, F2) for deflecting the probe stylus (2) out of its zero-position are dependent on the scanning direction of the probe stylus (2) on an object (O);

   when an object (0) is scanned with the free end of the probe stylus (2) in a first scanning direction, the measuring plate (10) may be tilted about a first rotational axis (D1), and in a second scanning direction about a second rotational axis (D2), the rotational axes (D1,D2) being at differing distances from the working line of the resetting force (F12);

   opposite the free end of the probe stylus (2) lies a sensor (7, 8,9) which detects the deflection of the probe stylus (2) from its zero-position caused by scanning the object (0) and converts it into a stroke (15) in which a deflection signal may be generated, the deflection paths (SA1, SA2), which lead to the generation of the deflection signal, being inversely proprotional to the above-mentioned forces (F1, F2), characterised in that

   the deflection paths of the end of the probe stylus (2) to deliver the deflection signal upon tilting about the two rotational axes (D1, D2) are at least roughly identical, the differing deflection paths caused by the geometrical arrangement of the support points (14, 16) being compensated by the deformation of the assembly probe stylus (2)/support (17), by the geometrical layout of the support (17), the geometrical design of the probe stylus (2) and the characteristics of their materials - i.e. the deformation parameters of the assembly probe stylus (2)/support (17) - being matched to one another.
2. Multi-coordinate touch probe according to claim 1, characterised in that the working line of the resetting force (F12) is the central axis of the probe stylus (2).
3. Multi-coordinate touch probe according to claim 1 or 2, characterised in that three support points (14, 16) are distributed uniformly along the circumference, and in that the first rotational axis (D₁) is at a distance (l₁) from the working line of the resetting force (F₁₂) and the second rotational axis (D₂) is at twice the distance (l₂) from the working line of the resetting force (F₁₂).
4. Multi-coordinate touch probe according to claim 3, characterised in that the different deflection paths are compensated by the bending of the probe stylus (2), the diameter (T_D) of the probe stylus (2) being selected at least approximately according to the following relationship: TD 4 = F12·l1 2·L2·64·2l5·3E·π where

   F₁₂ =

   resetting force

   l₁ =

   distance of the first rotational axis from the working line of the resetting force (F₁₂)

   L₂ =

   length of the probe stylus (2)

   l₅ =

   stroke

   E =

   elasticity module of the probe stylus material

Images